Semiconductor devices are generally made by repeating unit processes, such as an ion implantation process, a thin film deposition process, and a heat treatment process, several times. The heat treatment process of the unit processes is applied to a process of thermally oxidizing a substrate, a process of thermally diffusing implanted ions, and various annealing processes. Specifically, as examples of the heat treatment process, there are annealing for restoring crystallinity after implanting impurity ions, annealing for improving the characteristics of the interface between a silicon (Si) film and a silicon oxide (SiO2) film, sintering for forming silicide, etc.
As heat treatment apparatuses for performing those heat treatment processes, there are furnaces, rapid thermal process (RTP) apparatuses, and so on. Particularly, the RTP apparatuses have advantages of obtaining desired effects using high temperatures, and performing a heat treatment process in a short time (in generally, several tens seconds to about several minutes) to minimize a side effect of impurity generation, and thus are being widely used for heat treatment processes.
The heat treatment apparatuses use heating lamps such as tungsten halogen lamps (0.8 μm to 4 μm) to apply heat to silicon substrates, and measure the temperatures (energy states) of the substrates with pyrometers. In the apparatuses, heat controllers receive the measured values as feedback, and control the heating lamps.
FIG. 1 is a schematic diagram for explaining a low-temperature heat treatment apparatus. As shown in FIG. 1, in a state where a substrate 20 has been safely placed on a substrate supporting portion such as an edge ring 30 in a process chamber 10, heat treatment is performed with a plurality of heating lamps 61, and the temperature of the substrate 20 is measured in a non-contact manner with pyrometers 40 for measuring a long-wavelength range. Hereinafter, a pyrometer means a pyrometer for measuring radiant energy of a long-wavelength range of 5 μm to 15 μm and converting the radiant energy into a temperature.
Therefore, the pyrometers 40 can collect the radiant energy, emitted from the substrate 20 and having a long wavelength of 5 μm to 15 μm and low temperatures of 500° C. or less, through lenses 41, and calculate the temperature of the substrate in a non-contact manner on the basis of the relation between black body radiation and temperature. The temperatures calculated in the pyrometers 40 are fed back to a heating unit 60 through a heating controller 50, such that temperature control is performed on the plurality of heating lamps 61.
Meanwhile, a pyrometer 40 of a RTP apparatus uses a wavelength range of 0.9 μm to 1.1 μm to measure temperature, and the measurement span of the pyrometer is about 450° C. to 1250° C. Meanwhile, the transmittance of the substrate which is measured by a pyrometer using the wavelength range of 0.9 μm to 1.1 μm depends on the temperature of the substrate. For example, at 25° C. (room temperature), the transmittance of the substrate is about 0.6, and at 500° C. or greater, the substrate has the transmittance of 0 (opacity).
In other words, the material of a silicon substrate transmits light at a temperature less than 500° C. or less. Therefore, in a case where the temperature of the substrate is less than 500° C., a part of light of the heating lamps passes through the substrate. Therefore, in the case where the temperature of the substrate is less than 500° C., a part of light of the heating lamps passes through the substrate, and thus the pyrometers cannot measure the accurate temperature of the substrate, resulting in an temperature measurement error. In other words, in the case where the temperature of the substrate is less than 500° C., the wavelength generated at the substrate itself and the wavelength of the light having passed through the substrate are added and measured in the pyrometers. For this reason, the present heat treatment apparatus cannot measure the accurate temperature of the substrate at a temperature less than 500° C., and thus cannot perform a rapid heat process at a low temperature.